Abstract
For the detection of an anomalous crustal deformation above the subduction zone, it is necessary to closely grasp the physical space-time characteristic lengths observed by the high accurate repetitional geodetic surveys, considering the limit of accuracy of obtained data and referring to various crustal deformation models given by many researchers. Especially, it is necessary to give a definite view on the substantial qualities from the space-time pattern in the secular variation of crustal movements basing on the recent detailed data of crustal structure. In this report, as an example of the investigation, Miura and Boso peninsulas are selected because many geodetic data on them have been accumulated since 1923 Great Kanto Earthquake (M7.9). These peninsulas are confronted with the Philippine sea plate and located under the influence of the Pacific plate and moreover, their tectonic beha viors show the various fluctuations due to these subducting plates. We call them "Time Dependent Peninsula Tectonics (TDPT)" and have been investigating them mainly by geodetic means to detect a uniform deformation in the various fluctuations through the subduction process. The outline of this investigation on the TDPT is as follows;(1) the secular variation related to some periodic change in elevation indicates the pos sibility of about 19-20 years variation. From this result, the long term earthquake prediction along the Japan trench suggested by FUJITA (1978) [1] may become possible in some aspects.(2) the intermediate term variation related to the subducting process indicates the im portance of the plate bending in the E-W direction of the Philippine sea plate due to the subduction of the Pacific plate. Then, recent deep earthquakes near the plate boundary are regarded as a phenomenon in releasing the increasing bending stress of the Philippine sea plate from the Pacific plate.(3) the annual variation related to seasonal change in groundwater or tide indicates the possibility of tidal loading effect. This result, however, is investigated now in detail. Such an investigation on the TDPT through geodetic means including detection of seasonal variation will be a great help in solving the problem on short-range earthquake prediction for practical use in the Kanto-Tokai area, though there are many points which must be solved.
